Motor drive system and linkage for hand prosthesis

ABSTRACT

A motor drive system and linkage arrangement for a hand prosthesis, wherein the prosthesis has at least one finger member extending generally tangentially with respect to a worm gear wheel secured to the prosthesis and driven by a drive motor and a worm gear located longitudinally within the finger to engage the teeth of the tangential worm gear wheel. When the drive motor runs the worm gear, the finger moves around the worm gear wheel toward or away from another finger member and/or a natural finger to open and close the prosthesis hand&#39;s grip. In an alternate embodiment, the drive motor and worm gear arrangement contained in one finger is connected by a linkage to the root portion of at least one other motorless finger mounted for pivotal movement on the prosthetic hand.

FIELD OF THE INVENTION

The present invention relates to hand prostheses and in particular tosuch prostheses with movable gripping fingers.

BACKGROUND OF THE INVENTION

The design of such hand prostheses presents formidable problems inachieving gripping light enough to handle fragile objects and strongenough to provide a secure grip to objects where it is desired to applysubstantial forces. These problems are further compounded by the limitedspaced available, especially within the fingers themselves, and where itis required to provide for independent movement of different fingers toa greater or lesser extent, and/or varying the rate of movement ofindividual fingers.

A particular problem arises with the fitting of hand prostheses inpatients with relatively long hand stumps. Conventional electrical handprostheses use an electric motor mounted in the body structure of thehand itself. Some versions have the motor mounted axially parallel tothe long axis of the arm and others have the motor at 90 degrees to thisaxis. A variety of transmission systems are used to link motor andfingers e.g. lead screw and nut, or bevel and spur gears. Withoutexception these types of hand prosthesis require precise alignmentbetween motor and transmission system. This is usually achieved bylocating all the parts within a hand body consisting of an investmentcasting or other moulded structure. Such an arrangement is relativelycumbersome and the motor cannot be readily accommodated within thelimited space available in the main body of the prosthesis attached tothe patient's hand stump. Another disadvantage is that patients withsome residual digits cannot have any functional restoration at allbecause of the space constraints. The operational characteristics ofsuch devices also tend to be restricted e.g. allowing only a singlegripping pattern to be employed.

SUMMARY OF THE INVENTION

It is an object of the present invention to avoid or minimise one ormore of the above disadvantages.

The present invention provides a prosthesis for providing at least onemechanically operable finger member, said prosthesis having at least onesaid finger member extending generally tangentially with respect to afixed worm gear wheel means on a support body of said prosthesis andmounted for rotation about the worm gear wheel spindle, said fingermember having a drive motor with a worm extending generallylongitudinally of the finger member and in engagement with the gearteeth of said worm gear wheel so that when said drive motor is operated,in use of the prosthesis, said finger member moves around said worm gearwheel towards or away from another finger member and/or a natural fingerfor closing and opening of a hand grip.

Thus the hand prosthesis of the present invention uses a particularlycompact form of finger drive which also can allow improved operationalflexibility.

As used herein the expression "finger member" includes a "thumb member".Whilst it is possible to provide a useful hand grip defined by just onemovable finger member and one fixed member, it is generally preferred tohave a hand prosthesis with a plurality of movable finger members, mostpreferably with control means formed and arranged so as to permit moreor less, independence of movement of the finger members or groups offinger members, e.g. to allow higher speed lower torque movement of a"thumb" finger member, and slower speed higher torque movement of theother finger(s), and/or to permit the provision of different grippingpatterns with different combinations of individual/group finger movementcharacteristics.

Conveniently a root portion of said at least one said finger memberprovided with a drive motor is connected by a linkage means to the rootportion of at least one other (motor-less) finger member mounted forpivotal movement on said support body, said linkage means being formedand arranged for transmitting drive to said other finger member so as topivotally move said other finger member towards or away from said atleast one finger member provided with a drive motor during directmovement thereof by the drive motor for closing and opening of a handgrip.

Whilst this kind of arrangement may have less power and operationalflexibility than other forms of the invention in which separate motorsare used for different fingers, it does have the advantage of requiringfewer motors and less power consumption thereby providing a moreeconomical solution.

Various suitable motors having a relatively high power-to-weight ratioare known in the art including permanent magnet DC motors which have asubstantially linear relation between torque and drive current over areasonably wide range which facilitates control of the driving of thefinger member. Particularly suitable motors are available from MinimotorSA of Switzerland, especially their motors which have a diameter ofaround 8 to 17 mm. A further advantage of this type of motor is theavailability of a modular gearbox system coupled to the output shaft ofthe motor which allows different torque-output drive speed ratios to beselected simply by choosing from a range of gearboxes with differentratios. This has the advantage of facilitating the provision, in aprosthesis, of different gripping patterns by simply using differentgearboxes in different finger members.

In general it is preferred to have a faster moving lower torque thumbfinger member with slower moving higher torque other finger members asthis simplifies the provision of a cosmetically acceptable sheathing orcladding of the mechanical components of the prosthesis due to thereduced range of movement of the other finger members.

The compact form of drive motor and mounting thereof substantiallywithin the finger member being driven, particularly when said drivemotor is inside a thumb finger member, allows for a reduction in fingersize and hence a lighter construction, which is particularly desirablein application of the prosthesis to children. Moreover the compactnessallows fitting to longer stumps which include a mobile wrist without anyloss of wrist mobility and without making the hand appear too long.

Further preferred features and advantages of the invention will appearfrom the following detailed description given by way of example of somepreferred embodiments illustrated with reference to the accompanyingdrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of the principal components of the operatingmechanism of a hand prosthesis of the invention;

FIG. 2 is a partly cut-away view of one finger member of hand prosthesisusing the mechanism of FIG. 1;

FIGS. 3 (a) and (b) are perspective views of a second embodiment of handprosthesis of the invention; and

FIG. 4 is a rear view of the hand prosthesis shown in FIGS. 3 (a) and(b).

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 shows the principal components of the operating mechanism 1 of ahand prosthesis having a main body 2 which is securely fixed in use to apatient's hand stump (not shown) in generally known manner, and aplurality of finger members 3. The main body 2 has mounted thereon aplurality of fixed worm wheels 4 for engagement, each with a worm 5mounted in the base 6 of a respective finger member 3 to extendgenerally tangentially of the fixed worm wheel 4. The worm 5 is mountedon the drive shaft 7 of a gearbox and drive motor combination 8extending longitudinally of the finger member 3. The finger member 3 ispivotally connected 9 to the main body 2 for pivoting about the axis 10of the fixed worm wheel 4 so that when the motor 8 is actuated to drivethe worm 5, the worm travels around the circumference 11 of the fixedworm wheel 4. At the same time the distal end 12 of the finger member 3describes an arc indicated by the arrows 13 for opening and closing of ahand grip.

The motor 8 is powered by small rechargeable Nickel Cadmium batteries 14(shown schematically) which may be remotely mounted e.g. in the 4th and5th fingers (not shown) of the prosthesis or in any suitable spacebetween the stump (not shown) and the prosthesis.

The motor 8 is controlled by means of switches 15 actuated by eitherresidual digit movement or by wrist motion. Two switches may be used tocontrol both directions of rotation or alternatively one switch may, bybeing interfaced through suitable electronic circuitry, be used tocontrol both directions in a sequential or toggled manner. In additionto switches, pressure signals derived from force sensitive resistormaterial or signals derived from the electromyographic activity ofresidual muscle actions, may be used as control signals.

The main body 2 of the prosthesis itself may conveniently be in the formof a simple bar 16 with finger and thumb spigots 17, 18 extendingtherefrom. The pivotal mounting of the finger members 3 is effected vialugs 19 which depend from a generally tubular housing 20 in which aremounted the motor 8 and worm 5.

The components 2 of the prosthesis operating mechanism 1 can be clad inan overlay 21 of silicone rubber or the like to provide a moreaesthetically acceptable appearance as similar as practicable to anormal hand appearance, in generally known manner.

FIGS. 3 (a) & (b) and FIG. 4 shows a second embodiment of handprosthesis and will be described with reference to the embodiment shownin FIGS. 1 and 2 and indicated by like reference indicia with suffix `a`added. The operating mechanism 1a of a hand prosthesis has a main body2a (only partially shown) which is securely fixed in use to a patient'shand stump in generally known manner. The main body 2a has mountedthereon a single fixed worm wheel 4a for engagement with a worm 5amounted in the base 6a of a thumb finger member 3a to extend generallytangentially of the fixed worm wheel 4a. The worm is mounted on thedrive shaft of a gearbox and drive motor combination 8a.

The thumb finger member 3a is pivotally connected 9a to the main body 2afor pivoting about the axis of the fixed worm wheel 4a so that when themotor 8a is actuated to drive the worm 5a, the worm travels around thecircumference 11a of the fixed worm wheel 4a. The main body 2a haspivotally mounted 22 thereon also a pair of finger members 23. Thefinger members 23 have an inwardly depending lever 24 pivotallyconnected by a generally arcuate or cranked linkage member 25 to a lug19a which extends from the housing 20a in which is mounted the motor 8aand the worm 5a. As may be seen from FIG. 4 the pivotal plane of thethumb finger member 3a is inclined (generally by an inclined angle α ofaround 55° to 60°) relative to that of the finger members 23 to providea more natural arrangement.

It will be seen from FIGS. 3 (a) and (b) that when the motor 8a isactuated to drive the worm 5a, the worm travels around the circumference11a of the fixed worm wheel whilst driving the linkage member 25 againstthe inwardly depending lever 24 on the finger members 23 so as totransmit drive thereto so as to pivotally move the finger members 23towards or away from the thumb finger member 3a for closing (FIG. 3 (b))and opening (FIG. 3 (a)) of a hand grip.

As with the first embodiment described hereinbefore the components ofthe second embodiment of prosthesis can be clad in an overlay ofsilicone rubber or the like to provide a more aesthetically acceptableappearance, in generally known manner.

The compact form of finger drive and mounting thereof substantiallywithin the finger being driven thereby, as well as the essentialneutrality i.e. non-handedness of its configuration, allow anessentially modular approach to the construction of electricallyoperated hand prostheses. This in turn leads to a number of advantagesincluding one or more of reduced stockholding requirements as variousdifferent prostheses, including left and right handed ones and ones withdifferent numbers of mechanical fingers may be readily assembled from asmall number of common components. In addition different grip patternscan be readily achieved by use of suitable controls with the independentfinger drives, with the further advantage that there is no need tocompromise between grip force and speed of operation or movement.

The modularity and compactness of the units also allows individualfinger prostheses to be used e.g. in the case of congenital deformitiesof the type where one or more fingers, especially the middle fingerswhich are important to effective prehension, are missing.

Accordingly, I claim:
 1. A prosthesis having at least one mechanicallyoperable finger member, the finger member extending generallytangentially with respect to a fixed worm gear wheel on a support bodyof the prosthesis and mounted for rotation about a worm gear wheelspindle, the finger member having a drive motor with a worm extendinggenerally along a longitudinal axis of the finger member and inengagement with gear teeth on the worm gear wheel so that when the drivemotor is operated, in use of the prosthesis, the finger member movesaround the worm gear wheel towards or away from another finger memberand/or a natural finger for closing and opening of a hand grip.
 2. Aprosthesis according to claim 1 wherein a root portion of at least onefinger member is provided with a drive motor connected by a linkagemeans to a root portion of at least one other finger member mounted forpivotal movement on the support body, the linkage means being formed andarranged for transmitting drive to the other finger member so as topivotally move the other finger member towards or away from the at leastone finger member provided with a drive motor during direct movementthereof by the drive motor for closing and opening of a hand grip.
 3. Aprosthesis according to claim 2 wherein the drive motor is a permanentmagnet D.C. motor having a substantially linear relation between torqueand drive current.
 4. A prosthesis according to claim 3 wherein thedrive motor is coupled to a gearbox system whereby in use differenttorque-output drive speed ratios may be selected from a range ofgearboxes with different ratios.
 5. A prosthesis according to claim 4having a plurality of finger members and provided with control meansformed and arranged so as to permit independence of movement of at leastone of the finger members with respect to other of the finger members.6. A prosthesis according to claim 5 wherein the plurality of fingermembers includes a single thumb finger member having a drive motor withhigh speed, low torque characteristics and at least one other fingermember having a drive motor with low speed, high torque characteristics.7. A prosthesis according to claim 6 clad with an overlay ofaesthetically acceptable material having an appearance generally similarto a normal hand appearance.
 8. A prosthesis according to claim 5,wherein the control means is formed and arranged so as to permitindependence of movement of a first group of the finger members withrespect to a second group of the finger members.